The invention relates to a multiphase thermoplastic composition which has an improved flexibility, impact strength, especially at low temperature, and delamination behaviour.
The invention relates especially to a thermoplastic composition consisting of a phase containing at least one thermoplastic resin and at least one ethylene polymer which has units derived from unsaturated epoxide or unsaturated acid anhydride, the said phase being dispersed in a matrix based on a thermoplastic resin. The invention also relates to a process for the preparation of the thermoplastic composition.
A further subject of the invention is the articles obtained from the said composition.
Compositions with a polyamide or polyester matrix and ethylenic polymers are already known for their impact strength.
Patent EP 096 264 describes a material of high impact strength, containing:
a thermoplastic nylon which has a relative viscosity of 2.5 to 5, and
from 5 to 60% by weight, relative to the thermoplastic nylon, of an uncrosslinked terpolymer consisting of:
55 to 79.5% by weight of ethylene,
20 to 40% by weight of at least one primary or secondary alkyl (meth)arcylate, and of
0.5 to 8% by weight of a functionally acidic monomer (for example maleic anhydride).
Patent EP 218 665 describes compositions containing from 50 to 95% by weight of at least one polyamide resin and 5 to 50% by weight of at least one ethylene polymer containing from 0.9 to 16 mol % of units derived from maleic anhydride and/or at least one alkyl acrylate or methacrylate in which the alkyl group has from 1 to 6 carbon atoms.
The said ethylene polymer is present in the form of a mixture of ethylene/alkyl (meth) acrylate copolymer (A) and of ethylene/maleic anhydride/alkyl (meth)acrylate terpolymer (B), the molar ratio (A)/(B) being between ⅓ and 3.
Document EP-A-072,480 is also known, which describes an impact-resistant composition including from 50 to 90% by weight of polyamide, from 1 to 45% by weight of an ethylenic ionomer resin and from 0.5 to 40% by weight of an elastomeric ethylenic copolymer.
U.S. Pat. No. 3,373,223 describes a polymer blend consisting essentially of 25 to 90% by weight of polyolefin, 5 to 70% by weight of polyamide and 1 to 10% by weight of an ethylene/(meth)acrylic acid copolymer.
Patent EP 268287 describes an impact-resistant composition including:
(a) a thermoplastic polyester
(b) 1 to 100 parts of a polymer containing at least one epoxy group per molecule and having a flexural elasticity modulus of not more than 104 kg/cm2 at ambient temperature, and
(c) 0.5 to 100 parts of a copolymer of xcex1-olefin and of an xcex1,xcex2-unsaturated carboxylic acid, in which at least 5 mol % of the carboxylic groups are neutralized with an alkali metal,
the parts being parts by weight per 100 parts by weight of the compound (a).
Patent EP 382539 describes a polyamide resin composition including:
(A) 60 to 97 parts by weight of a polyamide resin containing at least 2 parts by weight of a polyamide resin which has an end COOHs/end NH2S ratio of at least 1.5,
(B) 3 to 40 parts by weight of an ethylene terpolymer including 0.3 to 10% of maleic anhydride units, 5 to 60% of alkyl acrylate units and 40 to 90% of ethylene units, and 0.01 to 20 parts by weight per 100 parts by weight of the sum (A) and (B) of a crosslinking agent which is a polyfunctional compound containing at least two groups which are reactive towards the anhydride groups of (B).
In this composition a part of the polyamide resin (A) forms the matrix, the terpolymer (B) forms a so-called first-order disperse phase and the remainder of the polyamide resin of (A) forms a so-called second-order disperse phase.
Although these compositions exhibit an improved impact strength when compared with the polyamide matrix employed by itself, this improvement remains, however, insufficient for many applications requiring an excellent impact strength, especially at low temperature.
Furthermore, because of the crosslinking, these compositions exhibit high flexural moduli, and this is unacceptable when compositions which have a high flexibility are being sought.
The present invention provides a multiphase thermoplastic composition comprising a mixture (I) that includes at least one ethylene polymer (A) which has units derived from unsaturated epoxy monomers or from unsaturated acid anhydride monomers, and at least one thermoplastic resin (B) which is partially encapsulated by the said ethylene polymer (A). According to the invention, the mixture (I) is dispersed in a matrix that includes at least one thermoplastic resin (C), wherein the respective melting temperatures of the thermoplastic resins (B) and (C) are such that thermoplastic resin (B) remains partially encapsulated by ethylene polymer (A) during the manufacture or use of the composition. The present invention also provides methods for the manufacture and use of the compositions of the invention.